1. Field of the Invention
This invention relates to a new production method of a high magnetic permeability alloy film composed of iron, aluminum, and silicon.
2. Description of Prior Art
Recently, advancement in the recording density has become necessary in the field of magnetic recording technology in order to adapt to the diversification of the information to be recorded. It has also become necessary to obtain a magnetic head having a narrower track width and a narrower gap length, and including a material of a high magnetic permeability and a high saturation magnetization.
A Sendust alloy composed of iron, aluminum and silicon has been well known to be suitable as a magnetic head material because it has a high magnetic permeability, a high saturation magnetization and good wear resistance.
It has been well known that the magnetic permeability of an alloy of the iron-aluminum-silicon system varies largely with the composition thereof. Alloys of the iron-aluminum-silicon system which shows narrow and sharp peaks of a magnetic permeability are known as Sendust alloys. A Sendust alloy for practical use is usually composed of 6 wt % Al, 9.5 wt % Si and the remainder of Fe. On producing a Sendust alloy film, the control of the composition thereof is an essential problem in order to obtain an excellent magnetic characteristics. The term "Sendust alloy" will hereinafter be referred to a high magnetic permeability alloy in a rather broad range of the composition in the iron-aluminum-silicon system.
Conventionally, the following methods have been used to produce a Sendust alloy film. (1) A process of polishing a bulk Sendust alloy into a film of a predetermined thickness. (2) A sputtering method of preparing a Sendust alloy film of a predetermined thickness. (3) A rapidly quenched method to form a Sendust alloy film. However, those methods have disadvantages as follows. As for the first method, it is difficult to cut and to dice a bulk material because of the brittleness thereof. It is also difficult to control the film thickness precisely. The second method is not appropriate to form a relatively thick film because of its very slow deposition rate. Finally, the third method does not allow control of the film thickness precisely because the film thickness is easily influenced by the processing conditions. The brittleness and the largeness of grain size of a rapidly quenched film remain still to be solved; the former causes troubles in a shaping process, and the latter limits the frequency characteristics. A rapidly quenched film is adhered with a plastic between nonmagnetic substrates in a fabrication process of a magnetic head. It is difficult to make the adherence layers as thin as possible in this process.
The inventors have already disclosed a new production method of a high magnetic permeability alloy film, wherein an alloy material composed of 1-6 wt % Al, 20-35 wt % Si and the remainder of iron is evaporated with the irradiation of an electron beam in a vacuum deposition apparatus equipped with an electron gun, and the vapor of the alloy material is deposited on a substrate for a predetermined time needed to adjust the composition of the deposited film to that of a high magnetic permeability alloy. Furthermore, it is preferable for a deposited film to be kept between 400.degree. and 800.degree. C. for a predetermined time for the heat treatment. The vacuum deposition process has several advantages as follows. The deposition rate is so high as to be suitable for the mass production of magnetic head cores. A deposited alloy film can be used as a magnetic head core and allows the fabrication of a magnetic head with both a narrow gap and a narrow track width without any further processing. A Sendust alloy film produced according to the present invention has superior high frequency characteristics.
However, the process should be improved in order to produce a high magnetic permeability alloy film of better quality. For example, an alloy material will be contaminated by impurities in the process of preparing a tablet thereof in a crucible under vacuum. It is also important to improve the frequency characteristics of a thick film for a magnetic head core material.